As used in the present context, the term "SIM" includes a data card, such as a smart card (IC card or magnetic card), and other forms of package enclosing or carrying a memory device. In addition to subscriber identity information, such as the subscriber telephone number, and personal identification number (PIN), the smart card may store for example, call charge information (i.e. a charge meter), a telephone number index, or false PIN entries. As memory capacity expands in smaller chip sizes, more application can be implemented on one smart card. Accordingly, it is envisaged that in future multipurpose smart cards will cover an even wider range of applications than personal identification and data storage services.
Indeed, in modern telecommunications systems, the applications for smart cards is expanding. One such application in this field is the SIM proposed for the pan-European digital cellular radio telephone system known as GSM (Groupe Speciale Mobile). For more information about the SIM proposed for GSM, reference is invited to the European Telecommunications Standards Institute (ETSI) Recommendations GSM 11.11 which describes the technical SIM specifications and Recommendation GSM 02.17 for the functional characteristics of the SIM.
There are currently two different mechanical standards proposed for the GSM SIM card and it is probable that a third will evolve. The functionality of the SIM is the same for all sizes, it is essentially that the physical dimensions are different. At present the two standards are (a) a credit card size SIM, and (b) a plug-in SIM about 20 mm.times.25 mm. The proposed third standard is likely to be a mid-sized SIM about half the size of a regular credit card. The rationale behind the different sizes is that the credit card size is perceived as a convenient size for the user from a practical standpoint. However, the credit card size is relatively large, and smaller card sizes are needed as miniaturization continues to drive down the overall size of the terminal (i.e. the radio telephone unit itself). The plug-in SIM is intended to be semi-permanently installed in the cellular telephone.
The implementation of data services specified by GSM has not generally been considered necessary by GSM operators in the initial stage of the service. In this situation those customers who wish to obtain some kind of data services must rely upon other, simpler services provided by GSM.